Chemical dyes are important compounds for a range of applications. For example, inkjet inks typically comprise at least one colorant in the form of a dye. Many dyes are charged molecules carrying either a positive or negative charge, which is balanced with a counterion. The present invention specifically relates to cationic salts of sulfonated dyes, such as sulfonated phthalocyanine dyes.
Sulfonated phthalocyanine dyes are useful in inkjet ink applications. For example, sulfonated copper phthalocyanines are well-known cyan dyes. More recently, the present Applicant has shown that sulfonated gallium naphthlocyanines are useful IR dyes having minimal visibility and excellent ozonefastness. Accordingly, sulfonated gallium naphthlocyanines have found utility in the Applicant's Netpage and Hyperlabel™ systems.
The Netpage and Hyperlabel™ systems generally require a substrate having a position-coding pattern printed thereon. The coding pattern is preferably printed with an IR-absorbing ink having minimal visibility, so that it does not interfere with the visible content of the substrate. A user can interact with the substrate using an optical sensing device, which reads part of the coding pattern and generates interaction data. This interaction data is transmitted to a computer system, which uses the data to determine what action is being requested by the user. For example, a user may make handwritten input onto a form, click on a printed hyperlink, or request information relating to a product item. This input is interpreted by the computer system with reference to a page description corresponding to the printed substrate.
Position-coding patterns for Netpage and Hyperlabel™ may be printed by analogue (e.g. offset) or digital (e.g. inkjet) printers. If the position-coding pattern is printed using an inkjet printer, it is important that the printhead has excellent longevity. Preferably, an IR channel in the printhead, used for printing the coding pattern, should have at least as good longevity as other color channels used for printing graphics, text etc.
Kogation is a term used to describe a phenomenon whereby residues are deposited over time on a heater element in an inkjet printhead. Kogation typically occurs from repeated firing of a heater element and is generally understood to result from high-temperature deposition of ink component residues. Usually, the inkjet dye (or pigment) is responsible for kogation on inkjet heater elements.
Therefore, an important characteristic of inkjet inks in thermal inkjet printing is their propensity to kogate on a heater element. Ideally, an inkjet dye should exhibit minimal kogation, which consequently improves the lifetime of an inkjet printhead.
One approach to minimizing kogation is to add relatively large amounts of surfactant or other additives to the ink vehicle. For example, U.S. Pat. No. 6,533,851 describes phosphonate additives for inkjet inks, which are claimed to reduce kogation. However, additives of this type generally compromise print quality by increasing intercolor bleed.
Another approach to the problem of kogation is to simply ignore the kogate and ‘overpower’ the heater elements so that water is superheated through the kogate. This approach is unsatisfactory in the Applicant's Memjet® printheads, which use minimal ink ejection energy for each nozzle so as to achieve high-speed pagewidth printing. Overpowering each nozzle would inevitably compromise print speed and/or nozzle density.
It would therefore be desirable to provide an inkjet dye, which exhibits reduced kogation. It would be further desirable to provide an IR-absorbing inkjet dye, which exhibits reduced kogation.